1. Field of the Invention
The invention relates to a truing device that includes a truer that corrects the shape of a grinding wheel in a grinding machine that grinds a workpiece with the use of the grinding wheel.
2. Discussion of Background
Some grinding machines are provided with a truing device that corrects the shape of the grinding surface of a grinding wheel in order to machine a workpiece into a predetermined shape or in order to maintain appropriate grinding efficiency. For example, Japanese Patent Application Publication No. 6-210565 (JP 6-210565 A) describes a swiveling truing device as the above-described truing device. The swiveling truing device swivels a rotatable rotary truer about an axis perpendicular to a central axis of a grinding wheel to carry out truing of the grinding wheel. In the swiveling truing device, the truing edge position of the truer (the truing edge position of the outer peripheral surface when viewed from the radial direction, in the case of a rotary truer) may be deviated from a control position used in truing due to an installation error of a support member for the truer, abrasion of the truer itself, or the like.
In a truing device of a grinding machine, the influence of the above-described positional deviation of the truer needs to be reduced in order to improve the accuracy of truing. Therefore, JP 6-210565 A describes a method of detecting the position of the outer peripheral surface of the grinding wheel with the use of a contact sensor before and after truing, and making a correction based on the detected positions to carry out subsequent truing. More specifically, JP 6-210565 A describes a method of calculating the outside diameter of the grinding wheel on the basis of the values detected by the contact sensor and then calculating the amount of abrasion of the truer on the basis of the outside diameter of the grinding wheel. According to this method, at the time of the subsequent truing, the operation of a grinding wheel head that is synchronized with the swiveling operation of the truer is corrected on the basis of the amount of abrasion of the truer. Therefore, the positional deviation of the truer is reduced to carry out truing with higher accuracy. In addition, Japanese Utility Model Application Publication No. 6-3561 (JP 6-3561 U) describes a truing device that is provided with contact sensors (electric micrometers) that contact a truer to detect the truing edge position of the truer. With this truing device, the movement amount of the truer is corrected on the basis of electric signals from the contact sensors to correct a positional deviation of the truer.
However, in the method described in JP 6-210565 A, the amount of abrasion of the truer is indirectly calculated on the basis of the outside diameter of the grinding wheel. Therefore, deviation factors, such as a rotation runout of the grinding wheel and a thermal displacement of a grinding machine, may influence the detection by the contact sensor. Furthermore, in the truing device, the position of the outer peripheral surface of the grinding wheel at the time of detection by the contact sensor differs from the position of the outer peripheral surface of the grinding wheel that is positioned at the time of actual truing. Therefore, an error may be contained in the calculated amount of abrasion of the truer.
In addition, in the swiveling truing device, the influence of a positional deviation of the truer is particularly large when the sectional shape of the grinding wheel at the outer peripheral surface is formed into a curved surface shape, such as an arc shape. Therefore, it is necessary to detect the truing edge position of the truer using the swivel center as the reference position, and to correct the positional deviation of the truer more appropriately. The truing device described in JP 6-3561 U detects the truing edge position of the truer with the use of the contact sensors. Even if this configuration is applied to a swiveling truing device, the reference position does not coincide with the swivel center. Therefore, it is necessary to indirectly calculate the truing edge position of the truer with respect to the swivel center. Accordingly, the above-described deviation factors may influence detection by the contact sensors.